The invention generally relates to a process for improving the colorfastness of dyed thermoplastic textile materials, and textile materials having improved colorfastness. More specifically, the invention relates to a process for dyeing textile materials such as microdenier fibers and fabrics made from microdenier fibers, which provides the materials with superior colorfastness capabilities along with desirable strength and aesthetic characteristics.
Textile fibers are commonly used in a variety of end uses. In many cases, it is desired that the fibers provide certain visual and aesthetic characteristics, as well as particular functional characteristics. For example, fibers are commonly dyed to achieve particular colors, in order to provide a certain visual appearance to the products which they are used to make.
One problem associated with the dyeing of fibers is that it can be difficult in some cases to achieve good colorfastness while maintaining desired functional characteristics. To this end, the type of dye and processing method used to dye products must be selected to provide the desired end performance characteristics, and optimal levels of particular parameters may have to be sacrificed to achieve acceptable levels of other characteristics.
Recent developments in the synthetic fiber industry have enabled the production of finer denier fibers than heretofore achievable. Such filaments typically have a silkier feel than those of larger size, and therefore can be used to achieve fabrics having improved hand characteristics as compared with those formed from larger filaments. In particular, it has been found that other things being equal, a fabric made from a yarn bundle formed of a plurality of fine denier fibers will generally have a better hand than a fabric made from similarly-sized yarns made from larger denier fibers. Therefore, the demand for microdenier fibers and fabrics made from microdenier fibers continues to increase as their desirability is recognized by consumers and manufacturers.
One disadvantage associated with fine denier fibers (such as microdenier fibers, which are typically considered to be those which have a denier per filament ratio of 1.0 or smaller) is that it is typically more difficult to achieve an equivalent depth of shade when dyeing as compared with their larger counterparts. Such finer denier fibers generally have inferior colorfastness as compared with larger-sized fibers, particularly with darker, deeper shades of dye. As the size of a fiber (i.e. the denier per filament or xe2x80x9cdpfxe2x80x9d) decreases, the proportion of fiber surface area to total fiber composition increases. As a result, a greater percentage of colorant or dyestuff by weight is generally required to achieve an equivalent depth of shade as compared to that required for conventional larger sized fibers.
Dyeability can be particularly difficult to achieve for darker-colored fibers, as such colors typically require the application and retention of an even greater percentage of dye substance. For example, it is not uncommon for microdenier fibers to require the application or incorporation of as much as three times the amount of dyestuff or colorant as that required for larger fibers, in order to achieve a similar dark shade. Correspondingly, the microdenier fibers typically have lower colorfastness than their larger denier counterparts, which can present problems in their end use. For example, the dyes can be released during subsequent washing of the fibers or articles which they are used to make. Not only does this diminish the integrity of the color of the article, but the freed dye molecules can undesirably attach to other articles in the same wash bath, adversely affecting their color. For this reason, it can be difficult for manufacturers to provide single items incorporating distinct regions of highly contrasting colors, particularly when the regions include microdenier fibers, since the dyes of the darker region tend to bleed onto the lighter colored regions during laundering.
Current practices for addressing the problems associated with the poor colorfastness of microdenier fibers include utilizing expensive high fastness dyes, applying strong reductive chemicals to the fabric or yarn after dyeing, and/or heat treating the fabric to normal heatsetting temperatures (e.g. about 340xc2x0 to 380xc2x0 Fahrenheit for polyester) prior to dyeing. Each of these processes will be described more specifically below; all have proven to be insufficient in achieving good coloration and colorfastness on the most difficult shades.
As noted, high colorfastness dyes, which typically utilize benzodifuranone or thiophene structures, etc., can be used to improve colorfastness. However, they are typically much more expensive than conventional dyes. Therefore, it can be difficult to achieve dyed yarns and fabrics using these high colorfastness dyes at desirable levels of cost. Furthermore, the colorfastness achieved by such dyes is still below what would be optimal under normal processing conditions.
Another method for enhancing colorfastness of microdenier materials involves applying a strong reductive chemical to the fabric or yarn after processing. The reductive process or reductive xe2x80x9cclearxe2x80x9d as it is known, functions to clear and destroy the dye molecules which have not attached securely to the textile material, so that they are not later released. However, the chemicals used in the clearing process can fail to remove all of the weakly attached dye molecules, and therefore they often do not eliminate the problem. In addition, the reductive chemicals can have a deleterious effect on the strength of the fabric. Furthermore, subsequent processes such as drying or heatsetting can liberate additional dye molecules from the fiber structure.
A further method for attempting to enhance the colorfastness of microdenier materials involves pre-heat treating the material at normal heatset temperatures in order to stabilize it for dyeing. For example, polyester is typically heatset at a temperature from about 340xc2x0 F. to about 380xc2x0 F. (i.e. about 171xc2x0 C. to 193xc2x0 C.) and therefore a pre-heat treatment would generally be performed at these same temperatures. Generally, it is considered to be desirable to minimize the formation of highly crystalline regions, as such are considered to be undyeable. Therefore, it is usually considered to be desirable to minimize the temperature at which the fabric is heatset to the extent possible. This is especially true of microdenier fibers and microdenier fiber-containing fabrics because of the aforementioned problem of greater surface area increasing the dye requirement. An improvement of this method is disclosed in commonly-assigned co-pending U.S. patent application Ser. No. 09/472,694 for xe2x80x9cProcess for Making Dyed Textile Materials Having High Colorfastness, and Materials Made Therefrom.xe2x80x9d
A further method for attempting to enhance the colorfastness of microdenier materials involves pre-heat treating the material at normal heatset temperatures in order to stabilize it for dyeing. For example, polyester is typically heatset at a temperature from about 340xc2x0 F. to about 380xc2x0 F. (i.e. about 171xc2x0 C. to 193xc2x0 C.) and therefore a pre-heat treatment would generally be performed at these same temperatures. Generally, it is considered to be desirable to minimize the formation of highly crystalline regions, as such are considered to be undyeable. Therefore, it is usually considered to be desirable to minimize the temperature at which the fabric is heatset to the extent possible. This is especially true of microdenier fibers and microdenier fiber-containing fabrics because of the aforementioned problem of greater surface area increasing the dye requirement. An improvement of this method is disclosed in commonly-assigned co-pending U.S. patent application Ser. No. 091472,694 for xe2x80x9cProcess for Making Dyed Textile Materials Having High Colorfastness, and Materials Made Therefromxe2x80x9d, filed Dec. 27, 1999.
It has also been proposed to enhance fiber colorfastness through the application of chemistry designed to assist in dye retention. For example, one manufacturer has proposed the application of a polysiloxane and organo-tin combination according to specific application processes. The proponents of the polysiloxane/organo-tin combination maintain that the polysiloxane/organo-tin compound is activated by temperatures of 340xc2x0-380xc2x0 (i.e., normal heatset temperatures for polyester). They therefore teach that the compound must be applied to the fabric and subsequently heatset. One problem associated with this method is that it typically results in a shade change from the original dyed color of the textile material, with the shade change often being severe.
While each of these practices and combinations thereof are considered to assist in improving the colorfastness of the microdenier materials, the colorfastness of such materials is still generally considered to be inferior to that of standard denier filaments. To further improve the colorfastness of microdenier materials, the finished fabrics are in some cases reloaded into a dye machine and treated with a reductive scour. In fact, in some cases it has been found that acceptable results can be achieved by this method. However, this process adds the steps of unrolling and batching a set for the dye machine, reloading and scouring, unloading, detwisting and drying, and therefore can be expensive to perform. Furthermore, this process reduces production dyeing capacity, adds length to the processing time and is not always successful. In addition, this method creates the risk of causing other off-quality characteristics and in some cases may change the material parameters through the use of so many additional processing steps.
Because of the difficulties associated with obtaining microdenier materials with good colorfastness as noted above, many manufacturers simply limit the depth of shades offered in connection with microdenier fabrics. As will be readily appreciated by those of ordinary skill in the art, this can be unacceptable from an end user""s standpoint, since this limits the designers"" creative freedom in designing new product offerings.
In the following detailed description of the invention, specific preferred embodiments of the invention are described to enable a full and complete understanding of the invention. It will be recognized that it is not intended to limit the invention to the particular preferred embodiment described, and although specific terms are employed in describing the invention, such terms are used in a descriptive sense for the purpose of illustration and not for the purpose of limitation.
The instant invention overcomes many of the disadvantages associated with the prior art constructions by achieving fibers having superior colorfastness properties, while retaining strength and other functional capabilities. In addition, the fabrics made by this method have been found to have a better hand than comparable fabrics made by prior art methods. Furthermore, the instant invention enables the achievement of products having superior colorfastness at reasonably comparable levels of cost to products having significantly inferior levels of colorfastness.
For purposes of illustration, the process will be described in connection with the dyeing of fabrics, and in particular, with the dyeing of polyester fabrics. It is noted, however, that the process is equally applicable to the processing of fibers or yarns, as well as other types of textile materials, within the scope of the instant invention.
The process involves providing or obtaining a textile material, which may be a textile fiber, a spun or filament yarn, or a fabric. Where the process is used in connection with the processing of fabrics, it may be in the form of a woven fabric, knit fabric, nonwoven fabric, or the like.
The fibers or yarns can have any size or denier desired. However, it has been found that the process of the instant invention performs particularly well in connection with the manufacture of microdenier fibers (i.e., those having a denier below one dpf) and yams and fabrics incorporating those fibers.
In addition, the textile material is desirably a thermoplastic material. For example, the process can be applied to thermoplastic components such as polyester, poly(trimethylene terephthalate) (xe2x80x9cPTTxe2x80x9d), polyamides, nylons, etc.
Depending on the manufacturing techniques used to produce the textile material and the type of end product desired, the textile material can optionally be de-sized and/or scoured to prepare it for processing. In addition, the textile material can be subjected to other forms of processing such as sanding, sueding, or the like at any stage in the process, but preferably prior to the application of the polysiloxane/organo-tin chemistry combination (which will be discussed further herein.) The textile material may also be heatset prior to dyeing if desired, depending on the end properties desired to be achieved.
The textile material is then desirably dyed to achieve a selected color. For example, the textile may be jet dyed, jig dyed, beck dyed, beam dyed or dyed in any conventional manner using time and temperature profiles designed to achieve a particular shade.
The textile material may then optionally be aftercleared by applying a reducing agent designed to remove excess dye molecules. The fabric may also be rinsed if desired, to ensure the removal of the reducing agent and loose but undestroyed dye molecules. For example, the material could be processed through a bath of sodium hydrosulfite to destroy the poorly attached dye molecules. In a preferred form of the invention, afterclearing is performed by applying 2.0% o.w.g. Soda Ash and 0.5% o.w.g. Thiourea Dioxide at 160xc2x0 F. In some cases, it has been found that superior colorfastness can be achieved even without the afterclear step, when the textile material is subsequently processed in accordance with the instant invention.
The textile material is also heatset in a conventional manner. As will be readily appreciated by those having ordinary skill in the art, xe2x80x9cheatsettingxe2x80x9d refers to the process of conferring dimensional stability to manufactured fibers, yarns and fabrics through the application of wet or dry heat. In other words, the temperature of the thermoplastic material is raised sufficiently above its glass transition temperature (which is specific to each type of thermoplastic material) so as to soften the polymer enough to rearrange or realign the polymer structure to the desired shape (e.g., as by the tension on the textile). For example, polyester is generally heatset at temperatures of about 340xc2x0 F. to about 380xc2x0 F. The heatsetting can be done before or after dyeing, although it will generally be preferred when processing knit fabrics to heatset after dyeing, in order to avoid de-knitting during the dye process or excessive curling of the fabric edges which can lead to uneven dyeing.
The textile material is then treated with a polysiloxane/catalyst combination. Preferably, this combination includes 1-10 g/L of polysiloxane along with a suitable catalyst. In a preferred form of the invention, the combination includes about 6 g/L polysiloxane and about 3 g/L of an organo-tin component. For example, this concentration has been found to work well in the processing of polyester materials, where a wet pick up of about 60% to about 65% is to be expected. However, as will be readily appreciated by those of ordinary skill in the art, the concentration can be adjusted with routine experimentation to achieve the optimal performance, depending on the type of material to be processed and its associated wet pick-up percentage, etc.
The textile material is then dried, preferably at relatively low temperatures. In a preferred form of the invention, the textile material is dried at a temperature which is at least about 15%, more preferably at least about 20%, and more preferably at least about 25% less than the temperature at which it is heatset. For example, in the case of a polyester material, the heatsetting is desirably performed at about 340xc2x0 F. to about 380xc2x0 F. and above, and the drying is performed at about 250xc2x0 F. to about 325xc2x0 F. Even more preferably, heatsetting is performed at about 370xc2x0 F. and drying is performed at about 220xc2x0 F. In most cases, it is generally preferred that the textile material is dried at a temperature of about 300xc2x0 F. or less, and more preferably about 275xc2x0 F. or less.
The thus-produced textile materials have superior colorfastness as compared with prior art dyed materials, particularly in connection with fine denier textile materials, including microdenier fibers. In fact, it has been found that a 4.0 or greater can be achieved on each fiber when tested according to AATCC Colorfastness Test Method 61 for most dye colors. As illustrated below, the process of the invention has been shown to increase the average washfastness rating of polyester microdenier fabrics an average of 0.5 point on polyester, 0.8 point on nylon, and 0.4 point on cotton, as compared with the ratings achieved by conventional methods. In addition, the high levels of colorfastness can be achieved even at relatively high levels of dye add-on. For example, it has been found that the 4.0 wash test results can be achieved on microdenier fabrics even when the dye add-on percentages are 3.5% o.w.g. or greater, 4.5% o.w.g. or greater, 6% o.w.g or greater, and even at 8% o.w.g. or greater.